Overwrite "cookie" in header throw exception in web player.

This problem appears in unity 4.3, and can only be reproduced in web player. I saw this post cookie header with unity 4.3 Somebody gave the solutions, though, they didn't work for me. I don't have much time to modify the server code to reattach another key word in header as a cookie to the request before authentication took place . As for delete library folder, it will make the unity editor return to PC platform settings, if I switch it back to web player, the problem still exist.

I guess it may be a bug in unity, however, I'm here for an temporary solution. Any ideas? Thx in advance.